The current methods used to measure the CSF are often unreliable, due to high variability between measurements. This study will compare four (4) new tests with two (2) currently used standard tests. The contrast sensitivity function will be measured using all of the six (6) methods three times (3) in each of the two (2) eyes at two (2) occasions. Each subjects CSF will be measured 6x3x2x2 = 72 times.